In the treatment of gold ores it has been found that the gold particles are quite often tarnished. Hedley and Tabachnick (Chemistry of Cyanidation, June 1958) state that the effect of such coverings is to retard dissolution in the cyaniding process and to increase gold losses. In addition these gold particles are difficult to amalgamate or to recover by flotation. Taggart (Handbook of Mineral Dressing, Sect. 2, p. 72, Wiley, 1945) reported that one type of nonamalgable gold ores was where the gold is coarse enough to amalgamate, but is so coated on the surface (rusty) that it is not wetted by the mercury.
The mechanism for the formation of the coating is not understood. Feather and Koen (Jnl. of South Africa Inst. of Mining & Metallurgy, Feb. 1973, pp. 223-234) found that free gold grains were enveloped in distinct coatings of hydrated iron oxide. Such coatings have an adverse effect on subsequent metallurgical processes such as cyanidation, amalgamation, and flotation and Feather and Koen stated that the loss of free gold is probably related to the heavy tarnish on the grains and to the effects of excessive milling (grinding). They reported that, "during ball milling copious quantities of finely divided iron are produced. From here onward, the iron plays its deleterious role in the circuit." Recommendations were made to minimize or prevent the formation of such coatings because of the adverse efffect on metallurgical processing.
The coatings render said particles magnetic or weakly magnetic. During the 1970's magnetic separation tests were carried out in South Africa to recover these weakly magnetic gold and uranium particles from tailings and residues by the use of wet high intensity-magnetic separation, the only known method for recovering these particles. The test results are discussed by Corrans and Levin (Jnl. of South African Inst. of Mining & Metallurgy, March 1979, pp 210-228) However, wet high-intensity magnetic separation has high operating and capital costs, is energy intensive in that it consumes much power, and has a low capacity compared to gravity or gravity-magnetic types of separators. A further disadvantage, reported by Corrans in an unpublished paper, is that wet high-intensity magnetic separators are subject to blockage due to wood chips and ferromagnetic materials (magnetite, pyrrhotite, and ilmenite) present in the slurries being treated. Another disadvantage is the low recovery achieved by the wet high intensity magnetic separation. Corrans and Leven reported in 1979 that the main source of loss was the inefficiency of the separator in the recovery of material smaller than 20 micrometers. In 1983, H. von Michaelis reported after an extensive review of methods for recovering gold, "the question might be asked whether iron coated gold could not be recovered by magnetic separation to make a concentrate for further treatment, but so far no commercial application of magnetic separation was found" (Society of Mining Engineers, American Institute of Mining & Metallurgical Engineers, Preprint 83-119, March 1983).
The lack of success in recovering the weakly magnetic gold particles by wet high intensity magnetic separation lead to the idea that the Gravity-Magnetic Separator (South African Pat. No. 84/2130, May 29, 1985; U.S. Pat. No. 4,565,624, Jan. 21, 1986), which recovers high specific gravity weakly magnetic minerals, would recover the weakly magnetic, high specific gravity gold particles. Furthermore, many gold ores are recovered by gravity concentration and fine-sized gold particles are lost to the tailings. In the paper cited above Feather and Koen reported that, "unfortunately, the particles of free gold and iron have by now acquired similar properties, and both are of high specific gravity." Gold has a specific gravity of 19.3 which makes it amenable to gravity separation, but this method is also inefficient in the recovery of small gold particles and those which are flaky. Therefore, instead of attempting to prevent or minimize the formation of coatings, a method has been provided to make the gold particles magnetic and using a Gravity-Magnetic Separator increase recovery of said gold particles.
The purpose of the invention is to provide a commercial, low cost, high capacity, environmentally safe process for the recovery of gold and/or uranium minerals from ores. A further objective is to recover gold and/or uranium minerals from tailings and residues that are now being discarded as to waste. Another purpose is to provide a process for economically treating gold and/or uranium tailings dump material.
The present invention is a process in which reagents, chemicals, or additives, both inorganic and organic are added to the slurry to cause the formation of a coating on the gold and/or uranium minerals present in the slurry of ore, tailings, or residue. Said coatings would be one that renders the desired species to be recovered to become magnetic or weakly magnetic. The new process uses means to accelerate said coatings to form, in contrast to present processes which attempt to prevent the formation of such coatings.
The treated slurries can be fed to a gravity-magnetic type separator, which is the subject of a U.S. pat. (U.S. Pat. No. 4,565,624, E. Martinez, Jan. 21, 1986). This type of separator will recover high specific gravity, weakly magnetic particles. It has a high capacity, low operating costs, and low energy requirements.
It may be necessary after making a concentrate of the gold and/or uranium particles by this new process to remove the coating for subsequent metallurgical treatment. Treatment of the concentrates with acid, such as hydrochloric acid, or other reagents may be required.
One of the advantages of the invention is that it provides a physical procedure for concentrating gold and/or uranium minerals from ores, tailings, or residues. A further advantage is that it provides an environmentally safe method for recovery of gold and/or uranium minerals. Another advantage is that it provides a comparatively simple and inexpensive procedure for effecting such a separation. Another important advantage is that the invention permits the exploitation of lower grade ores than would be possible in the absence of the invention. Another advantage is that it permits the recovery of values now lost in the tailings of existing operations. A further extremely important advantage of the invention is that it permits the useful life of the mine to be extended.
These and other advantages will become apparent from the following more detailed description of the invention.
Accordingly, it is an object of the present invention to provide a means for recovering gold and uranium minerals by rendering said particles magnetic or weakly magnetic by the addition of suitable chemicals or reagents so that said particles can be concentrated or recovered by means of a gravity-magnetic type separator (U.S. Pat. No. 4,565,624, E. Martinez) or other suitable magnetic type separator.